"I want to repeat what I said last night: There is no cause for alarm," by the doctor's diagnosis Thursday, said Mayor Bill de Blasio, even as officials described Spencer riding the subway, taking a cab and bowling since returning to New York from Guinea a week ago. "New Yorkers who have not been exposed to an infected person's bodily fluids are simply not at risk."

Bellevue Hospital personnel in protective suits in an isolation room during an Oct. 8 demonstration of procedures for Ebola patients. (AP Photo/Richard Drew)

The Centers for Disease Control and Prevention confirmed the city's Ebola diagnosis for Spencer, said Dr. Mary Bassett, the city's health commissioner. And a company contracted to handle medical waste arrived at his Harlem apartment.

Heath officials have repeatedly given assurances that the disease is spread only by direct contact with bodily fluids such as saliva, blood, vomit and feces, and that the dried virus survives on surfaces for only a matter of hours.

But some in the nation's most populous city, with more than 8 million people, were not taking any chances.

Friday morning, a group of teenage girls in Catholic school uniforms riding the L subway train passed around a bottle of hand sanitizer. They said they were taking extra precautions because of the Ebola case. It was one of the subway lines the doctor rode after returning home.

The governor and health officials said Spencer, a member of Doctors Without Borders, sought treatment with diarrhea and a 100.3-degree fever - not 103 as officials initially reported Thursday night. The health department blamed a transcription error for the incorrect information. He was being treated in an isolation ward at Manhattan's Bellevue Hospital, a designated Ebola center.

Veronica Lopez, who lives in the building next to the doctor, said "people were joking about it" but when the doctor's diagnosis was announced they "went crazy." She said she heard the city was notifying residents via fliers "and my roommate was freaking out because we didn't get a flier."

But Tanya Thomas, 47, who lives in Spencer's building, was matter-a-fact about the whole thing.

"He's the one with Ebola," she said. "If I get it, I get it."

Health officials say the chances of the average New Yorker contracting Ebola are slim. Someone can't be infected just by being near someone who is sick with Ebola. Someone isn't contagious unless he is sick.

Bassett said the probability was "close to nil" that Spencer's subway rides would pose a risk. The bowling alley has been cleared to open, she said. Spencer's Harlem apartment is cordoned off but no other tenants are at risk, officials said.

Evageline Love also was unconcerned. "I saw the mayor and the governor. What they're saying, I believe, is true. There's no need for hysteria," she said as he rode the L train to work.

The Centers for Disease Control and Prevention, which will do a further test to confirm the initial results, has dispatched an Ebola response team to New York. President Barack Obama spoke to Cuomo and de Blasio on Thursday night and offered the federal government's support. He asked them to stay in close touch with Ron Klain, his "Ebola czar," and public health officials in Washington.

Spencer's fiancee and two friends had been quarantined, but showed no symptoms, officials said.

The epidemic in West Africa has killed about 4,800 people. In the United States, the first person diagnosed with the disease was a Liberian man, who fell ill days after arriving in Dallas and later died, becoming the only fatality. None of his relatives who had contact with him got sick. Two nurses who treated him were infected and are hospitalized. The family of one nurse said doctors no longer could detect Ebola in her as of Tuesday evening.

According to a rough timeline provided by city officials, in the days before Spencer fell ill, he went on a 3-mile jog, went to the High Line park, rode the subway and, on Wednesday night, got a taxi to a Brooklyn bowling alley. He felt tired starting Tuesday, and felt worse on Thursday when he and his fiancee made a joint call to authorities to detail his symptoms and his travels. EMTs in full Ebola gear arrived and took him to Bellevue in an ambulance surrounded by police squad cars.

Doctors Without Borders, an international humanitarian organization, said per the guidelines it provides its staff members on their return from Ebola assignments, "the individual engaged in regular health monitoring and reported this development immediately." Travelers from Guinea, Liberia and Sierra Leone must report in with health officials daily and take their temperature twice a day, as Spencer did. He also limited his direct contact with people, health officials said.

Spencer, 33, works at NewYork-Presbyterian/Columbia University Medical Center. He had not seen any patients or been to the hospital since his return, the hospital said in a statement, calling him a "dedicated humanitarian" who "went to an area of medical crisis to help a desperately underserved population."

Four American aid workers, including three doctors, were infected with Ebola while working in Africa and were transferred to the U.S. for treatment in recent months. All recovered. Health care workers are vulnerable because of close contact with patients when they are their sickest and most contagious.

In West Africa this year, more than 440 health workers have contracted Ebola and about half have died. But the Ebola virus is not very hardy. The CDC says bleach and other hospital disinfectants kill it.

Spencer is from Michigan and attended Wayne State University School of Medicine and Columbia's University Mailman School of Public Health.

According to his Facebook page, he left for West Africa via Brussels last month. A photo shows him in full protective gear. He returned to Brussels Oct. 16.

"Off to Guinea with Doctors Without Borders," he wrote. "Please support organizations that are sending support or personnel to West Africa, and help combat one of the worst public health and humanitarian disasters in recent history."